Questions about the Light Path node
Question 1:
Light Path node outputs a single value between 0 and 1.
When plugged directly into RGB input, they correspond to black and white.
Example using the mentioned Ray Length output. The longer the distance, the higher the value.

Question 2:
The values are calculated for each ray hitting a surface.

Direct view - 0 bounces
Mirror reflection - 1 bounce
Glass panes - 1 to 3 bounces